Existing methods of constructing towers used to support different types of equipment, such as lighting, antennae, cellular telephone equipment or wind turbine equipment, vary depending on whether the tower materials are steel or concrete. The decision process used to select whether the tower is to be built out of steel or concrete may depend upon the geographic location, regional resources, height and weight bearing requirements for the tower, and access to the site for constructing the tower. Steel towers are commonly built by bolting steel tubular sections together at intermediate flanges. Generally, as the height of a tower increases, the diameter of the tower's base increases to accommodate higher loads generated by the taller tower. The heights of steel towers are often limited by the diameter of the steel tubular sections that can be physically transported to the construction site without significant modifications to existing roads, bridges, or other right of way constraints. Transporting large diameter steel tubular sections and associated components also increases the cost of tower construction.
Concrete towers have advantages over steel towers because they can be fabricated at or near the tower location when the materials of construction are locally available. Cast-in-place construction methods allow for pouring concrete into forms erected at the tower location. Drawbacks to cast-in-place methods include reduced construction speed and sensitivity to inclement weather. Also, the shape of a typical concrete wind tower is tapered, which creates complexity in the concrete pouring process. Alternatively, concrete tower sections can be fabricated or precast and then stacked at the job site to form the tower. Joints between tower segments may require grout to ensure sufficiently strong connections, and it may be necessary to pump grout to tower heights of up to 300 feet or more, which is time consuming, requires specialized equipment and is weather dependent, thereby adding cost to the tower construction.
U.S. Pat. No. 8,720,139 B2 issued on May 13, 2014, to Henderson describes a post-tensioned concrete foundation for supporting a tower whereby a base flange of the tower is set in grout inside a grout trough molded by a template ring extending around the top surface of the foundation cap. The tower may be plumbed vertically by shim packs positioned in the grout trough below the base flange while grout is poured or pumped into the grout trough under the flange and cured. The template ring may be positioned with respect to a tower anchor bolt cage to form a grout trough during the concrete pour. The template ring may then be removed and reused for the formation of grout troughs of other concrete foundations. A tower or other structure may then be secured in place within the grout trough with an appropriate amount of grout placed therein. This creates a connection where the tower base flange is secured with post-tensioning anchor bars directly within the grout trough of the concrete foundation.